WASHINGTON (CNN) -- U.S. officials say international inspectors have uncovered evidence North Korea may have supplied Libya with a key ingredient used in making nuclear weapons.

However, the officials stressed the evidence is not conclusive and the matter is still under investigation.

The ingredient in question is uranium hexafluoride, which can be used to produce enriched uranium for nuclear weapons.

If proved, this would be the first indication North Korea is a possible supplier in the clandestine nuclear network, and is generating concern other nations such as Iran might be in cohorts with Pyongyang.

Inspectors looking into Libya's now-abandoned nuclear program had been working on the theory that the material may have been supplied by Pakistan.

The South Asian nation has already been implicated in a worldwide nuclear black market, with the father of its nuclear program, Abdul Qadeer Khan, admitting earlier this year that he sold secrets to a number of nations, including Libya, North Korea and Iran.

U.S. officials have said previously that North Korea sold Scud missiles to Libya, using the proceeds to develop its own nuclear weapons.

Earlier this month, the Libyan government announced it would halt military trade with North Korea.

The possible North Korean-Libyan nuclear link was first reported Sunday in the New York Times. The report said Pyongyang provided Libya with nearly two tonnes of uranium in early 2001.

The White House could not confirm the report but was aware of it, said spokesman Trent Duffy.

"That is why it is important we continue with our policy of making sure North Korea disarms in a complete, irreversible and verifiable fashion," Duffy said, adding coalition partners needed to work together to stop illicit trading of weapons of mass destruction.

In January, Libya turned over equipment it was using to build a nuclear bomb to the United States, after the country's leader, Col. Moammar Gadhafi, announced he was giving up his pursuit of weapons on mass destruction.

Since then, nuclear inspectors have been investigating the sources of the material.

Pyongyang, which Washington has labeled part of an "axis of evil," is believed to have processed enough nuclear fuel to manufacture several nuclear weapons

Japan and North Korea, along with the United States, Russia, China and South Korea, are involved in six-party talks aimed at getting Pyongyang to give up its nuclear ambitions.

North Korea has said it will freeze its nuclear program as a first step in resolving the dispute, but only if the United States lifts sanctions, resumes oil shipments and removes the nation from its list of countries sponsoring terrorism.